Advances in Fish Tagging and Marking Technology

Advances in Coded Wire Tag Technology: Meeting Changing Fish Management Objectives

Geraldine Vander Haegen, Lee Blankenship, and Dave Knutzen


Abstract.—Coded Wire Tags (CWT) are lengths of magnetized stainless steel wire 1.1 mm long and 0.25 mm in diameter with a code etched along the wire. The tags are injected internally and while their presence can be detected electronically, code recovery requires that the tag be read under a microscope. CWTs have been in widespread use since their invention in the 1960s and their ongoing importance has been partly due to technological advances that meet the needs of fish management and research. We describe three changes in CWT technology that we think have played the most important roles. First was a coding format change from binary to decimal coding that made the tag code directly readable and reduced errors as well as providing a virtually unlimited code capacity. Second was the development of the highly sophisticated AutoFish System for automated injection of CWTs and adipose fin clipping of salmonids without human handling or anesthetic. Finally, we describe the development of new tools for electronic detection of CWT that allows tagged animals of any species to be sorted from untagged animals.